Interpretive Summary: This paper evaluates barriers to seed production in crapemyrtle.Several cultivars were found to have defective pollen but all had sufficient viable pollen to achieve seed set. Effectiveness of self- and cross-pollinations was assessed by comparing pollen tube growth, seed-pod set, seeds per pod and seed germination. Seed pod set and germination were much lower for self-pollinations as compared to cross-pollinations. Pod set after self-pollinations ranged from 33.6% to 3.7% . Germination of seed generated by self-pollinations was very low ranging from only 4% to 8%. When decreased pod set is combined with much lower germination for self-pollinations, selfing of crapemyrtle is extremely unproductive when compared to cross-pollination.

Technical Abstract:
The objectives of this study were to evaluate barriers to successful seed production in crapemyrtle. Male fertility was determined by staining pollen to determine viability. Effectiveness of self- and cross-pollinations was assessed by comparing pollen tube growth, seed-pod set, seeds per pod and seed germination. Over 90% of the pollen of Acoma, Arapaho, Catawba, Osage, Whit IV and Tuscarora stained indicating high viability while approximately 50% of the pollen of Whit VII and Apalachee and 70% of the pollen of Tonto appeared non-viable. Viability of all cultivars was sufficient to achieve pollination. Observation of pollen tube growth after self- and cross- pollination at intervals up to 24 hrs found no barriers to self-fertilization acting at the stigmatic or stylar level in L. indica or interspecific crosses with L. fauriei. Seed pod set and germination were significantly lower for self-pollinations as compared to cross-pollinations for Catawba, Whit IV, Tonto and Tuscarora evaluated as female parents. Pod set after self-pollinations ranged from 33.6% for Catawba to only 3.7% for Tonto. Germination of seed generated by self-pollinations was very low ranging from only 4% to 8%. When decreased pod set is combined with much lower germination for self-pollinations, selfing of crapemyrtle is extremely unproductive when compared to cross-pollination. A late-acting self-incompatibility system or inbreeding depression is indicated for L. indica and interspecific crosses with L. fauriei.